[R(Cl)GaAs(SiR&#39;3)2 ]n

ABSTRACT

A novel gallium arsenide precursor has the formula R 2  GaAs(SiR&#39;) 2  wherein R is selected from the group consisting of alkyl substituted cycloaliphatic group and alkyl substituted aromatic group and R&#39; is alkyl. Preferably, R is pentamethylcyclopentadienyl and R&#39; is methyl. The precursor is reacted with an alcohol, preferably ethanol or t-butanol at a temperature ranging from -20° C. to 60° C., preferably at room temperature, under water free conditions to form solid gallium arsenide and by-products which are liquid under the reaction conditions. The gallium arsenide forming reaction may be aided by a catalyst providing amount of a substance which is considered to react with excess alcohol reactant to generate a catalytic amount of HCl, e.g., (CH 3 ) 3  SiCl or [R(Cl)GaAs(SiR&#39; 3 ) 2  ] n  wherein R is pentamethylcyclopentadienyl and R&#39; is methyl and in solution in benzene n is 1 and 3.

This invention was made with Government support under Grant No. CHE8451670, awarded by the National Science Foundation. The Government hascertain rights in the invention.

This is a divisional of co-pending application Ser. No. 07/307,995 filedon Feb. 9, 1989 now U.S. Pat. No. 4,902,486 which is acontinuation-in-part of Ser. No. 07/116,212 filed on Nov. 3, 1987 nowU.S. Pat. No. 4,879,397.

TECHNICAL FIELD

This invention is directed to novel arsinogallane compounds and to amethod of preparing gallium arsenide therefrom.

BACKGROUND OF THE INVENTION

The common method for synthesizing gallium arsenide is known as themetal organic chemical vapor deposition (MOCVD) method and involvespassing gaseous trimethyl gallium and a large excess of gaseous arsinedown a tube to deposit gallium arsenide on a heated substrate. Thismethod has the disadvantage of relying on large quantities of a verytoxic gas, arsine, and very high reaction temperatures, namely 600° C.to 700° C.

Another method for forming gallium arsenide is disclosed in Gallagher etal U.S. Pat. No. 4,399,097 wherein a complex having the formula Ga_(a)(NH₄)_(b) H_(c) (AsO₄)_(y) is reduced in a hydrogen atmosphere at anelevated temperature, typically in the range of 400°to 900° C. Whilethis method avoids use of toxic arsenic containing reactants in gaseousform since the complex is prepared utilizing arsenic pentoxide, it alsohas the disadvantage of requiring very high reaction temperatures.

Jensen U.S. Pat. No. 4,594,264 discloses forming gallium arsenide byapplying a liquid film of gallium arsenic complex of the formula X₃GaAsR₃ in solvent, evaporating the solvent and irradiating. This methodhas the disadvantage of requiring an evaporation step after complex isisolated and requires irradiating (A laser is the only means forirradiating which is specifically named).

SUMMARY OF THE INVENTION

It has been found herein that novel gallium arsenide precursors can beprepared and converted into gallium arsenide without use of gaseousarsenic-containing compounds, high temperatures, an evaporation stepafter precursor isolation or irradiation.

The novel gallium arsenide precursor herein is arsinogallane compoundhaving the formula R₂ GaAs(SiR'₃)₂ wherein R is selected from the groupconsisting of cycloaliphatic group, alkyl substituted cycloaliphaticgroup and alkyl substituted aromatic group, and R' is alkyl.

To form gallium arsenide, the precursor is reacted with alcohol presentin excess and having the formula R"(OH)_(x) wherein R" is alkylcontaining from 1 to 10 carbon atoms and x ranges from 1 to 3, at atemperature ranging from -20° C. to 60°C. under water free conditions.The gallium arsenide is formed as a solid which precipitates underreaction conditions while the by-products are liquid or dissolved underthe reaction conditions so that the gallium arsenide is readilyrecovered.

DETAILED DESCRIPTION

We turn now in detail to the gallium arsenide precursor having theformula R₂ GaAs(SiR'₃)₂.

In said formula, cycloaliphatic group or moiety of R can be, forexample, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl,cyclononyl, norbornyl,2,2,2-bicyclooctyl, cyclobutenyl, cyclopentenyl,cyclopentadienyl, cyclohexenyl, cyclohexadienyl, norbornyl,cycloheptenyl, cycloheptatrienyl, cyclooctadienyl and cyclopentadecenyl.

In said formula, aromatic moiety of R can be, for example, phenyl orindenyl.

In said formula, alkyl substituent of R can be one or a plurality of thesame or different straight chain or branched chain alkyl groups.Preferably each said alkyl substituent contains from 1 to 5 carbonatoms. Very preferred alkyl substituent of R comprises a plurality ofmethyl groups.

In said formula, preferred R groups include, for example,pentamethylcyclopentadienyl, mesityl and 1-norbornyl.

In said formula, R' preferably contains from 1 to 5 carbon atoms and canbe straight chain or branched chain. Very preferably R' is methyl.

The precursor R₂ GaAs(SiR'₃)₂ is readily prepared by reacting (R₂ GaCl)₂with LiAs(SiR'₃)₂ wherein R and R' are defined as above. This reactionis readily carried out utilizing stoichiometric amounts of the reactantsat a temperature ranging from -20° C. to 60° C. in a solvent which canbe aliphatic hydrocarbon, aromatic hydrocarbon or ether solvent.Substantial completeness of reaction is obtained over a period of about2 hours at -20° C. to less than a minute at 60° C. Preferably, thisreaction is carried out at room temperature, e.g., 26° C. to 28° C., andsubstantial completeness of reaction is normally obtaIned in 2 to 10minutes. Suitable solvents include, for example, pentane, cyclopentane,hexane, cyclohexane, methylcyclohexane, heptane, benzene, toluene,xylene, tetrahydrofuran, dimethyltetrahydrofuran, diethyl ether,dimethoxyethane, and dioxane. Preferred solvents are benzene andpentane. The reaction should be carried out in the absence of watersince water reacts with the starting materials and formed precursor. Inthe reaction the formed precursor R₂ GaAs(SiR'₃)₂ remains dissolved inthe reaction solvent and by-product lithium chloride, precipitates.Precursor R₂ GaAs(SiR'₂)₂ is readily obtained in substantially purifiedform by removing the resulting solution from the precipitated lithiumchloride by-product, for example, by filtering, stripping solvent fromR₂ GaAs(SiR'₃)₂ product, for example, at room temperature under vacuumand recrystallizing from hydrocarbon solvent, e.g. pentane at -35° C.The reaction is preferably carried out under an inert atmosphere, e.g.,under dry nitrogen, to preclude the presence of moisture.

The starting material (R₂ GaCl)₂ is readily made by the method describedin Beachley et al, Organomet. 4, 1675 (1985). The starting materialLiAs(SiR'₃)₂ is readily prepared by reacting arsenic with 1.90equivalents of sodium and 1.56 equivalents of potassium indimethoxyethane, e.g., at reflux temperature for 36 hours, and thenreacting at reflux temperature with ClSiR'₃ thereby to form As(SiR'₃)₃and reacting this product with methyllithium in tetrahydrofuran. Thepreparation of LiAs(SiMe₃)₂ where Me is methyl is described in Becker,G., et al, Z. Anorg. Allg. Chem, 462, 113 (1980).

A preferred arsinogallane (gallium arsenide precursor) has the formulaR₂ GaAs(SiR'₃)₂ wherein R is pentamethylcyclopentadienyl and R' ismethyl. This compound is a yellow crystalline solid having a meltingpoint of 112° C.-118° C. and a vapor pressure below 1.75×10⁻⁵ torr. at298° K. (so it does not easily vaporize and is easily handled withoutdanger). It reacts immediately with water and slowly with oxygen.

We turn now to the reaction whereby the precursor R₂ GaAs(SiR'₃)₂ isconverted to gallium arsenide.

The reaction proceeds to produce gallium arsenide as product whichprecipitates from the reaction solution and RH and R"OSiR'₃ asby-products (R,R' and R" are defined as above) which are liquid and/orsoluble in the reaction solution.

The alcohol reactant R"(OH)_(x) for this conversion reaction can bestraight chain or branched. Suitable alcohols include, for example,ethanol, propanol, isopropanol, n-butanol. s-butanol. t-butanol.ethylene glycol, pinacol, glycerin, and phenol. Preferred alcoholreactants are ethanol and t-butanol. Since the reaction to form galliumarsenide is conducted in the absence of water, absolute alcohols shouldbe used as reactants.

Preferably this reaction to convert precursor to gallium arsenide iscarried out at room temperature; e.g. 26° C.-28° C.

The reaction to convert precursor to gallium arsenide is carried out tosubstantial completeness in several, e.g., 12 hours at -20° C. to lessthan a minute, e.g., in 30 seconds, at 60° C. At room temperature thereaction is carried out to substantial completeness in a period of about1 minute to about 1 hour with shorter times being a function of theamount of excess of the alcohol reactant and the concentration of thealcohol reactant in the reaction solution: a reaction tIme of up to 12hours or more can be useful when the alcohol reactant is used in astoichiometric amount.

Preferably the alcohol reactant is present in an amount of 2 to 100equivalents per equivalent of arsinogallane (precursor) reactant.

The reaction to convert precursor to gallium arsenide is readily carriedout in a solvent selected from the group consisting of aliphatic,aromatic and ether solvents. Very suitable solvents include pentane,cyclopentane, hexane, cyclohexane, methylcyclohexane, heptane, benzene,toluene, xylene, trahydrofuran, dimethyltetrahydrofuran, diethyl ether,dimethoxyethane, and dioxane. Toluene, benzene and pentane are preferredsolvents. The reaction solvent is selected so that gallium arsenideproduct precipitates from the reaction solution and so that by-productRH and R"OSiR'₃ are liquids under the reaction conditions or dissolvedin the reaction solvent. Protic and halogenated solvents should not beused.

The reaction to convert precursor to gallium arsenide is preferablycarried out under an inert atmosphere, e.g., under dry nitrogen, topreclude to presence of moisture.

The reaction to convert precursor to gallium arsenide is aided by acatalyst providing amount of a substance which is present with theprecursor as an impurity and/or which is added which is considered toreact with excess R"(OH)_(x) to generate a catalytic amount of HCl.

One catalyst providing substance is (CH₃)₃ SiCl used in an amount, forexample, ranging 1/10 to 1/2 mole per mole of precursor. Addition inamount of about 1/3 mole per mole of precursor has been found to speedthe reaction by a factor of about 3.

Another catalyst providing substance is obtained by reacting R₂GaAs(SiR'₃)₂ wherein R is pentamethylcyclopentadienyl and R' is methylwith 1 equivalent of HCl at room temperature and has been assigned thecomposition [R(Cl)GaAs(SiR'₃)₂ ]_(n) and wherein R ispentamethylcyclopentadienyl and R' is methyl and wherein in solution inbenzene n is 1 and 3 so that there is present approximately equalweights of monomer and trimer. This (both the monomer and trimercomponents) reacts instantaneously with t-butanol to yield galliumarsenide and thus in addition to providing a catalyst provides product.This is used, for example, in an amount ranging from about 1/50 mole toabout 1/2 mole per mole of precursor. Use in an amount of about 1/10mole per mole of precursor has been found to speed the reaction by afactor of about 10. Both said monomer and said trimer as well as thecombination thereof are considered to have catalyst providing effect.

The formed gallium arsenide, as indicated above, is the only reactionproduct to precipitate from solution and is readily recovered byseparating the precipitate from the reaction solution, e.g. by filteringor evaporating solvent and by-products. The gallium arsenide product isrecovered as a substantially pure reddish-brown, amorphous powder bywashing, e.g. with solvent for by-products, preferably pentane ortoluene followed by tetrahydrofuran and then heating under vacuum at,for example, 100° C. to remove residual solvent.

The amorphous gallium arsenide product may be used in solar cells, orthe amorphous product can be converted to crystalline form by methodsknown in the art, e.g , by annealing at a temperature ranging from 200°C. to 1238° (m.p.). The crystalline material is useful forsemiconductors.

Instead of recovering precipitated gallium arsenide in amorphous form,the reaction of the precursor with alcohol can be carried out in thepresence of crystalline gallium arsenide substrate to deposit formedgallium arsenide epitaxially on said substrate.

The invention is illustrated by the following specific example:

EXAMPLE

LiAs(SiMe₃)₂ wherein Me stands for methyl was prepared by the method ofBecker, G., et al, Z. Anorg. Allg. Chem., 462, 113 (1980).

(R₂ GaCl)₂ wherein R is pentamethylcyclopentadienyl was prepared by themethod by Beachley et al, Organomet., 4, 1675 (1985).

Approximately 16 ml of pentane Was introduced into a vial under nitrogenin a drybox. Into the vial Were then added first 0.608 mmole of the (R₂GaCl)₂ and then 0.608 mmole of the LiAs(SiMe₃)₂. The reaction mix wasthen stirred at room temperature for 1 hour to ensure completion ofreaction. Then a white precipitate was removed bY filtration. Thefiltrate was stripped of solvent under vacuum, to yield a yellow solid.This material was recrystallized from pentane at -35° C. to yield 0.10gm of yellow plates of substantially pure crystalline compound; R₂GaAs(SiR'₃)₂ wherein R is pentamethylcyclopentadienyl and R'is methyl.The structure Was confirmed by NMR, elemental analysis (calculated:%C=55.62; %H=8.62; Found: %C=55.95; %H=8.79), infrared, and molecularweight determination. Yield obtained was 63% of theoretical. The productwas a crystalline solid with a vapor pressure less than 1.75×10⁻⁵ torr.at 298° K. It dissolved readily in pentane, benzene, and tetrahydrofuransolvents. The melting point of the product was 112° C. to 118° C.

Product made a above was converted to gallium arsenide as follows:

Approximately 12 ml of pentane was introduced into a flask with sidearmunder nitrogen in a drybox. Into the flask was added 0.863 mmole R₂GaAs(SiR'₃)₂ where R is pentamethylcyclopentadienyl and R' is methyl,and the flask was capped with a septum. The flask was taken out of thedrybox and attached to a nitrogen bubbler through the sidearm. Twoequivalents (1.726 mmoles) of tert-butanol was added via syringe throughthe septum. The reaction mixture was stirred at room temperature for 12hours; then the flask was evacuated and brought back into drYbox At thispoint, the mixture appeared reddish-brown in color and a reddish-brownprecipitate was evident. In the drybox the solvent was evaporated toyield 0.108 g reddish-brown solid. The solid was washed with toluene andthen tetrahydrofuran and dried under the vacuum. The product wasconfirmed by analysis to be substantially pure gallium arsenide.

The gallium arsenide obtained was a reddish brown, amorphous (by X-raydiffraction) powder.

When in the above gallium arsenide preparation, 0.3 moles of (CH₃)₃ SiClis added to the reaction mixture, reaction is completed in about 4hours.

When in the above gallium arsenide preparation there is added 0.1 moleof [R(Cl)GaAs(SiR')₂ ]_(n) as described above, reaction is completed in1 to 11/2hours. [R(Cl)GaAs(SiR'₂ ]_(n) as described above was preparedas follows: In a drybox, a 100 ml flask was charged with precursor R₂GaAs(SiR'₃)₂ wherein R is pentamethylcyclopentadienyl and R' is methyl(0.545 g, 0.972 mmoles), 21 ml C₅ H₁₂, and a stir bar. A needle valvewas attached and the system degassed on the high vacuum line. Oneequivalent HCl (275 torr, 25° C., 67 ml, 0.972 mmoles) was condensedinto the flask. Upon thawing, the solution color was yellow and a redprecipitate was evident. After three days at room temperature, thesolution color was yellow-orange and a small amount of precipitate wasstill present. The solvent was evaporated and the system returned to thedrybox. The solid products were extracted with C₅ H₁₂, which was thenevaporated. The resulting orange solid was recrystallized at -30° C.from C₅ H₁₂. Orange crystals were isolated (0.103 g), which were againrecrystallized to yield 0.030 g (0.065 mmoles, 7%) colorless crystals. ¹H NMR (C₆ D₆): δ1.96 (s,45H), 0.56 (s,54H), 1.94(s,15H), 0.36(s,18H).The former two resonances correspond to the trimeric form, the lattertwo to the monomeric. Anal.: Calc'd. for C₁₆ H₃₃ AsClGaSi₂ : C, 41.62;H, 7.20; Cl, 7.68. Found: C, 41.44; H, 7.16; Cl, 7.85.

R₂ GaAs(SiR'₃)₂ wherein R is mesityl and R' is methyl is obtained bysubstituting an equivalent amount of (R₂ GaCl)₂ wherein R is mesityl forthe (R₂ GaCl)₂ above where R is pentamethylcyclopentadienyl.

R₂ GaAs(SiR'₃) wherein R is 1-norbornyl and R' is methyl is obtained bysubstituting an equivalent amount of (R₂ GaCl)₂ wherein R is 1-norbornylfor the (R₂ GaCl)₂ above where R is pentamethylcyclopentadienyl.

The precursors described above where R is mesityl and where R is1-norbornyl are readily converted to gallium arsenide by substituting anequivalent amount of each for the precursor where R ispentamethylcyclopentadienyl in the reaction with t-butanol describedabove.

The reactions convert R₂ GaAs(SiR'₃)₂ to gallium arsenide describedabove produce substantially equivalent results when an equivalent amountof absolute ethanol is substituted for the t-butanol.

The reactions to convert R₂ GaAs(SiR'₃)₂ to gallium arsenide describedabove produce substantially equivalent results when the same volume oftoluene or benzene is substituted for the pentane.

Other variations will be evident to those skilled in the art. Therefore,the scope of the invention is intended to be defined by the claims.

What is claimed is:
 1. Composition of matter selected from the groupconsisting of monomeric and trimeric forms of R(C1)GaAs(SiR'₃)₂ whereinR is pentamethylcyclopentadienyl and R' is methyl.
 2. Composition ofmatter which in solution in benzene has the formula [R(Cl)GaAs(SiR'₃)₂]_(n) where R is pentamethylcyclopentadienyl, R' is methyl and n is 1and 3 such that there is present substantially equal parts of monomerand trimer.